U.S Pat. No. 5,067,322, issued to David G. Beers for "Refrigerator With Spine Fin Evaporator", and assigned to the same assignee as the assignee of this application, discloses a spine fin evaporator for a refrigerator. The spine fins of the evaporator of the aforesaid Beers patent, which is incorporated by reference herein, provide a large heat exchange area per unit length of the evaporator conduit or tube. This increase in the heat exchange area per unit length of the evaporator tube enables the size of the evaporator to be reduced for a given size refrigerator, which increases the usable storage space of the refrigerator.
The air being refrigerated by the evaporator is laden with moisture, and the evaporator normally operates at frost collecting temperatures. This moisture laden air flows around the fins and frost tends to build up quickly at the inlet end of the spine fin evaporator. This build up of frost requires the evaporator to be defrosted fairly often, which reduces the overall operating efficiency of the refrigerator.
The spine fin evaporator of the present invention satisfactorily solves the frost build up problem through disposing the evaporator in a substantially vertical orientation with a generally oval spiral or race track configuration. The evaporator is formed in the race track configuration by having an elongated tube formed with elongated straight runs or sides and relatively large radius return bent ends. This provides a relatively large space between the elongated straight runs through which the air can flow to enhance the air flow. This results in greater heat exchange values between the air and the elongated straight runs of the evaporator and reduces the pressure drop of the air due to frost build-up.
Additionally, the relatively large radius of the return bent ends result in a lower pressure drop of the refrigerant in the evaporator in comparison with a serpentine evaporator. This is because the relatively large return bent ends change the direction of the refrigerant gas more gradually.
The preferred embodiments are vertical spirals of evaporator tubing, rather than the horizontal spiral configurations of some current evaporators. Such horizontal coiled evaporators are subject to "puddling" of liquid refrigerant which causes "liquid slugging" and greater pressure drop of the refrigerant.
Some embodiments of the spine fin evaporator of the present invention have elongated straight runs on at least one side of the evaporator offset or deflected inwardly towards elongated straight runs on the other side of the evaporator. In some embodiments, these offset or deflected elongated straight runs are staggered throughout the vertical length of the evaporator except for the lower end of the evaporator over which the air flows initially. In some embodiments, this bottom portion is open to provide enhanced frost tolerance. The deflection or offset of the elongated straight runs is staggered vertically so that there are portions of the vertical length of the evaporator in which the elongated straight runs are spaced from each other for varying distances.
Both sides of the evaporator may have elongated straight runs offset or deflected inwardly towards the elongated straight runs on the other side of the evaporator. Preferably, this offsetting occurs at staggered intervals from one side of the evaporator to the other so that the elongated straight run on only one of the two sides of the evaporator at any specific location is moved inwardly towards the other side of the evaporator.
It is well known to position a defrost heater adjacent the end of a refrigerator evaporator first exposed to moisture laden air and, in some situations, to place such a heater intermediate the ends of the evaporator. If desired, such defrost heaters may be used in conjunction with evaporators incorporating the present invention.